All About Ultrasounds

What's an Ultrasound?

If you're pregnant, chances are you'll have an ultrasound at some point. Read on to learn what ultrasounds are, why they're necessary, and what they feel like.

Ultrasounds are sound-wave pictures that help doctors see internal fetal and maternal structures. The ultrasound probe scans across the mother's abdomen or inside her vagina. The transducer transmits high-frequency sound waves that echo back and are transformed into a picture on a video screen. This picture shows the fetus inside the womb. Often, parents will be given a printout of the ultrasound to keep.

At six weeks' gestation, it's possible to see the baby's heartbeat. For many expectant parents, it's an added bonus that an ultrasound given after 20 weeks can sometimes identify the sex of the baby. However, in some cases it's not possible to see the baby's genitalia and parents are kept guessing.

Why Have One?

Ultrasounds have many applications in pregnancy, and up to 60 percent of expectant mothers receive at least one scan. According to the American College of Obstetricians and Gynecologists, ultrasounds are usually prescribed for the following reasons:

To establish the baby's age: Early in pregnancy, ultrasound helps accurately date a pregnancy, preventing unnecessary interventions. About 30 percent of pregnancies have dating errors. For dating purposes, an ultrasound scan should be performed prior to 20 weeks; it's typically scheduled between 12 and 16 weeks.

To identify fetal abnormalities: Because it allows the physician to see the baby's developing body in great detail, an ultrasound is key in the detection of fetal abnormalities. An anatomy scan is usually done at 18 to 22 weeks.

To determine the position and size of the baby: Toward the end of pregnancy, with an ultrasound, a doctor can see a baby in breech position and determine if the baby is too big to fit through the mother's pelvic cavity.

To detect multiple pregnancies: Scans help confirm multiple pregnancies and assess the babies' growth and health.

To perform chorionic villus sampling or amniocentesis, or to obtain a blood sample from the umbilical cord: An ultrasound helps safeguard certain genetic-testing procedures by allowing the doctor to ascertain the safest place to insert a catheter or needle.

To assess pregnancy complications such as bleeding or pain: Ultrasound helps the physician see the source of the bleeding and identify possible complications such as placenta previa.

What Preparation Is Needed?

After you make your appointment, your doctor will give you an instruction sheet telling you what you need to do. Generally, women who are less than 14 weeks pregnant will be asked to fill their bladder to capacity. Sound waves travel better through liquid, so a full bladder improves the quality of an ultrasound during early pregnancy. As a woman's pregnancy progresses, a full bladder is not as essential because the uterus and fetus are so large. But even then, some physicians ask their patients to come with a full bladder because transmission of the sound waves is better with fluid in the bladder.

Vaginal probes are used early in pregnancy (12 weeks and earlier) because sound waves don't pass through bone. The fetus is deep in the mother's pelvis in early pregnancy.

What Does It Feel Like?

The process is not painful. When you have an abdominal ultrasound, the doctor will smear a clear gel on the skin of your abdomen to help the device pass smoothly over the skin and improve transmission of the sound waves. Some doctors warm the gel. Otherwise you might get a chilly sensation from the cold gel on your skin. The doctor usually applies some pressure as she moves the transducer device along your abdomen. The transducer transmits sound waves that create a picture of the baby inside. If you're ticklish, you might find yourself challenged during this procedure. Take a deep breath and try to relax!

A vaginal ultrasound is done with a wand-shaped probe covered with a latex sheath (like a condom). The doctor will apply some lubricant and gently insert the ultrasound into your vagina. She will move the device to form the picture she needs on the ultrasound screen. The procedure doesn't hurt, but you might find it uncomfortable in the same way you might find a pelvic exam uncomfortable. Again, relaxation and focus are key. And don't be afraid to tell your doctor if you need her to stop and give you a minute to breathe.

One of the best parts about having an ultrasound is actually seeing your baby while he's still inside you. For many women, this is a turning point during which they feel even more bonded to the life they're nurturing.

Reviewed 11/02 by Elizabeth Stein, CNM

All content here, including advice from doctors and other health professionals, should be considered as opinion only. Always seek the direct advice of your own doctor in connection with any questions or issues you may have regarding your own health or the health of others.